1. Field of the Invention
This invention provides a method for maintaining and/or repairing a protective coating on an article exposed to high temperature atmospheres.
2. Description of the Prior Art
Components used in high temperature environments, such as those encountered in the high temperature zones (e.g., combustion chambers, turbine sections and exhasut ports) of jet engines, rocket motors and the like, often must be protected from destructive reaction with oxygen and/or the products of fuel combustion. This is conventionally accomplished by coating the portion of the component exposed to the high temperature atmosphere with a non-reactive material such as a refractory oxide, carbide or silicate.
Considerable effort is being expended in attempts to increase both the operating temperatures and service life of existing coatings. The principal barriers to improvements in performance of such coatings are loss of thickness resulting from volatilization and cracking and spalling of the coating caused by differences in thermal expansion between the coating and the coated surface.
Damage to the protective coating of a component of an engine, if not immediately corrected, will result in loss of the component, which often causes loss of the engine, and ultimately loss of the vehicle powered by the engine.
U.S. Pat. No. 2,811,467--Hull et al., filed Jan. 21, 1952, generally relates to a method for insulating component parts of an apparatus exposed to high temperature gases resulting from the burning of a fuel, comprising applying a precoat formation on the component parts and introducing into the fuel a substance which fluxes with the precoat formation to form semimolten insulating compounds on the component parts.
While it appears that the process of the Hull et al. patent would tend to somewhat insulate the exposed component parts, a reaction of the substance in the fuel with a precoat material, particularly a fluxing reaction, would not be desirable in the advanced engine systems of today. The high velocity, high shear gas flow to which modern components are exposed would tend to remove at least a portion of a semimolten coating, thereby rendering it inefficient or useless.